It is known to provide a motor vehicle with an electric machine that can be operated as an electric motor or as an electric generator. One such device is an integrated starter-generator that can be used as a motor to temporarily provide a torque boost to an engine to which it is driveably connected. One type of integrated starter-generator is a crankshaft integrated starter-generator (CISG) directly driving a crankshaft of an engine and another type of integrated starter-generator is a belt integrated starter-generator (BISG) driven by a belt, such as a front end accessory drive (FEAD) belt, that can also add torque to a crankshaft of the engine via the FEAD belt. The use of a CISG/ BISG to provide a torque boost to the engine results in a motor vehicle sometimes referred to as a “hybrid vehicle.” With a hybrid vehicle, the CISG/ BISG is not used to directly drive the motor vehicle on its own unlike the electric motor or motors used in a full hybrid vehicle. With a hybrid vehicle, a CISG/ BISG is used to provide a torque boost to the engine and for starting the engine.
A known method to improve fuel economy at the expense of low end torque performance is the lengthening of the transmission Final Drive Ratio (FDR). However, there is a limit to the amount of torque reduction that is acceptable while maintaining good driveability. Furthermore, an NVH (Noise Vibration Harshness) mode known as lugging caused by impulsive inputs due to delivering high combustion torques can be induced if too much torque is requested at low engine speeds when the gear ratio is too high. Upshift and Downshift decisions are therefore normally based on the maximum torque available at any given time to ensure good driveability and good NVH.